All publications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Stem cells (SCs) are defined as cells with the unique capacity to self-replicate throughout the entire life of an organism and to differentiate into various cell types of the body. Two well-known types of stem cells are embryonic stem cells and adult stem cells. Embryonic stem cells (ESCs) are extracted from 5-10 day old embryos called blastulas. Once isolated, ESCs can be grown in vitro and led to differentiate into various types of tissue cell (such as heart cells, liver cells, nervous cells, and kidney cells), after which they can be injected in specific tissues in order to regenerate the tissue.
Adult stem cells (ASCs) are undifferentiated or primitive cells that can self-renew and differentiate into specialized cells of various tissues and are found in any living organism after birth. ASCs have been isolated from various tissues such as the liver (oval cells) (Wang et al., 2003), the intestine (intestinal crypt stem cells) (Barker et al., 2008), muscles (satellite cells) (Kuang et al., 2008), the brain (neural stem cells) (Revishchin et al., 2008), and recently the pancreas (nestin positive pancreatic stem cells) (Burke et al., 2007). Umbilical cord stem cells and placental stem cells are considered ASCs.
The role of ASCs found in tissues (tissue stem cells) is to maintain and repair the tissue in which they are found, although recent studies have reported that ASCs from one tissue may have the ability to develop into cell types characteristic of other tissues. For example, oval cells in the liver were shown in vitro to have the ability to become insulin-producing pancreatic cells. (Yang et al. 2002) Nevertheless, the general view is that local stem cells are primarily involved in minor repair of the tissue in which they reside. In the case of significant injury or degeneration, the number of new tissue cells found in healing tissue far exceeds the capacity of local stem cells to duplicate and differentiate, suggesting that stem cells coming from other sites must be involved in the process of repair.
Although many tissues contain their own specific population of tissue stem cells, certain ASCs of key interest are those primarily found in the bone marrow and blood, Tissue stem cells are traditionally believed to be limited in their ability to differentiate into other tissues, however bone marrow stem cells (BMSC) were recently shown to have significant capability to become cells of other tissues.
It is difficult to freeze these processes in time to extract a cohesive, comprehensive portrait of regenerative mechanisms in the body. Nonetheless, enough information is available to affirm that different stem cells in the body, whether BMSCs, HSCs, marrow stromal cells (MSCs), multipotent adult progenitor cells (MAPCs), very small embryonic-like stem cells (VSEL), epiblast-like stem cell (ELSC) or blastomere-like stem cell (BLSC), constitute a broad component of the body's natural healing system. Since stem cells are capable of differentiating into a broad variety of cell types, they play an important role in the healing and regenerative processes of various tissues and organs. Bone marrow stem cells, including marrow stromal cells (MSCs), are released from tissues of origin, and circulate in a subject's circulatory or immune system to migrate into various organs and tissues to become mature, terminally differentiated cells. Therefore, enhancement of stem cell trafficking (i.e., release, circulation, homing and/or migration) can amplify these physiological processes and provide potential therapies for various pathologies. There are compositions and methods that utilize stem cell mobilization as a therapeutic approach. However, existing methods of promoting stem cell mobilization suffer from significant drawbacks, including poor kinetic performance, high cost, inconvenient methods of administration and unwanted side effects. One leading approach, injection of granulocyte colony-stimulating factor (G-CSF) or recombinant forms thereof, requires days to achieve peak circulating HSC numbers. The opposite problem exists with administration of interleukin-8 (IL-8), which acts only within minutes and has a short-lived effect on elevating circulating HSC levels in the bloodstream. (Frenette et al., 2000; Jensen et al., 2007) G-CSF and a different molecule, CXCR4 antagonist AMD3100, can have significant side effects, including hemorrhaging, rupturing of the spleen, bloody sputum, bone disorders, among others. Thus, there is a need in the art for an effective and convenient method for delivering stem cell mobilization agents to human subjects, to obtain positive clinical benefits without side effects and at a reduced cost.
Accordingly, the inventive compositions and methods disclosed herein enhance the release, circulation, homing and/or migration of stem cells within the body to promote healing and treatment of damaged tissues, as well as aid in the regeneration of tissues that suffer from some level of cellular loss, for greater vitality and reduced incidence of disease.